With such a method, the volume is set according to the noise level that is present in the area of the loudspeaker in such a manner that the sound reproduction level of the loudspeaker, that is the wanted signal level, is always a few Decibel (dB) above the noise interference level. In this manner, the wanted signal given off by the loudspeaker is perceived by the listener to remain at approximately the same volume, independent of the level of the surrounding noise. Especially for mobile operation of a loudspeaker, or the radio receiver, this results in a significant improvement in comfort, since the listener is not forced to constantly adjust the volume when the noise level changes often.
The control circuit used for adjusting the volume attempts to continuously minimize the difference between the audio frequency level and the noise level. For a stabilized control situation, the difference is minimal. However, if for instance a pause occurs in the audio signal and the noise level remains the same, the control voltage for the control circuit, taken from the level comparator circuit, suddenly assumes a high value, which increases the amplification factor of the control element, or decreases the attenuation of transmission of the control element respectively. If the pause is ended abruptly with a loud audio signal, the volume is briefly too high; a sound reproduction control operation occurs that is perceived as unpleasant. For this discussion, a pause is defined as a time span with a negligible audio signal level, for instance the pause between two words in a speech signal. To avoid the disturbing effects caused by the pauses, pauses must be recognized as such. When determining a pause with a threshold, it is of little use to define a fixed threshold, set sufficiently for the largest occurring noise levels. In such a case, in an audio signal selection with almost no interference (e.g., from a compact disk, i.e., a CD), low passages that are worth boosting would drop below such a threshold. On the other hand, with a fixed threshold optimized for low-interference signal sources, background noise of lower quality audio signal sources may be evaluated as wanted signals, and boosted.